The invention is based on an anti-skid brake system as defined hereinafter. An anti-skid system of this kind is already known from German Patent 1 655 383 (FIG. 5), in which the pressure fluid reservoir is embodied as a cylinder with a spring-loaded piston, and a pressure switch for switching the return pump on and off is connected to the return feed line downstream of the throttle in the pumping direction. The return feed pump is switched on when a pressure is reached that because of the characteristic of the spring disposed in the pressure fluid reservoir is equivalent to a predetermined pressure fluid volume in the pressure fluid reservoir. The return feed pump, which has a constant pumping volume, pumps the pressure fluid out of the pressure fluid reservoir into the master brake cylinder. The pedal of this master brake cylinder is forced back as a result. Excessively long, forceful pedal motion is perceived as unpleasant by the vehicle driver, however. To reduce this feedback, the throttle in the return feed line is provided, which limits the pumped flow of pressure fluid to a low value. If there is a particularly marked decrease in brake pressure in the wheel brake during an anti-skid control event, however, the action of the throttle can produce an excess of pressure fluid in the pressure fluid reservoir and a lack of pressure fluid in the master brake cylinder. This situation cannot be tolerated, for safety reasons.